In practice, calcium carbonate is used in huge quantities in the paper, paint, rubber and plastics industries for various purposes such as coatings, fillers, extenders and pigments for papermaking as well as aqueous lacquers and paints and in water treatment, and notably as a means of removing inorganic materials such as heavy metals and/or pharmaceutical waste such as polycyclic compounds, cholesterol and/or endocrine disrupting compounds (EDC).
With respect to precluding aggregation of calcium carbonate particles and enhancing the affinity of these particles with a substance to which the particles are being added, for example as a filler or flocculating agent, the physical and chemical properties of the surfaces of such calcium carbonate particles are amended by treating the calcium carbonate with fatty acid or a sodium salt of a fatty acid, resin acid or other acids.
In the art, several approaches for improving the chemical and physical properties of calcium carbonate have been proposed. For example, U.S. Pat. No. 4,219,590 describes a method for improving calcium carbonate by causing calcium carbonate particles to undergo contact reaction with an acid gas capable of reacting with calcium carbonate for finely uniformizing the calcium carbonate particle size and, at the same time, coating the surface of the calcium carbonate particles with the calcium salt of the acid of the acid gas. U.S. Pat. No. 6,666,953 B1 relates to a pigment, filler or mineral containing a natural calcium carbonate, treated with one of more providers of H3O+ ions and gaseous CO2, allowing a reduction in the weight of paper for a constant surface area without loss of physical properties when it is used as a pigment or coating filler for said paper. WO 99/02608 A1 describes a method of producing a high solids slurry of an acid-resistant precipitated calcium carbonate, wherein a solids slurry is treated with a chemical additive, such as sodium aluminate, in order to impart acid resistance to the calcium carbonate.
Additionally, U.S. Pat. No. 5,584,923, U.S. Pat. No. 5,647,902, U.S. Pat. No. 5,711,799, WO 97/08247 A1 and WO 98/20079 A1, respectively, describe calcium carbonate which is acid-resistant to enable its use as a filler material in the making of neutral to weakly acidic paper, and a process for producing this acid-resistant calcium carbonate.
Furthermore, WO 2005/121257 A2 discloses a method for producing a dry mineral pigment characterized in that it contains a product formed in situ by the multiple reaction of a calcium carbonate and with the reaction product or products of said carbonate with gaseous CO2 formed in situ and/or from an external supply; and with at least one compound of formula R—X. WO 2004/083316 A1 refers to mineral pigments containing a product formed in situ by the double and/or multiple reaction between a calcium carbonate and the reaction product or products of the said carbonate with one or more moderately strong to strong H3O+ ion donors and the reaction product or products of the said carbonate with gaseous CO2 formed in situ and/or coming from an external supply, and at least one aluminium silicate and/or at least one synthetic silica and/or at least one calcium silicate and/or at least one silicate of a monovalent salt such as sodium silicate and/or potassium silicate and/or lithium silicate, preferably such as sodium silicate and/or at least one aluminium hydroxide and/or at least one sodium and/or potassium aluminate, used in papermaking applications, such as mass filling and/or paper coating.
U.S. Pat. No. 5,043,017 relates to calcium carbonate, acid-stabilized by the addition to finely divided calcium carbonate of one of a calcium-chelating agent and a conjugate base, such as sodium hexametaphosphate, followed by the addition of an acid, such as phosphoric acid.
However, the prior art seems to be silent on economic methods for preparing and controlling high surface area materials and methods for controlling the particle size of materials allowing for the provision of specific calcium carbonate materials for the desired purpose. In particular, methods for preparing high surface area materials of the prior art require the use of high amounts and concentrations of medium-strong to strong acids (having a pKa of less than or equal to 2.5) to obtain a desired material having a high specific BET surface area. Additionally, the use of such medium-strong to strong acids necessitates the use of high safety requirements in order to minimize the danger to employees. Furthermore, the use of high amounts and concentrations of said medium-strong to strong acids also result in a high and cost-intensive consumption of chemicals and water.
Thus, it would be desirable to have a process available which allows for preparing surface-reacted calcium carbonate and provides the possibility of controlling particular parameters such as the specific BET surface area and particle size of the calcium carbonate.